This article investigates shelf space allocation in the marketing of manufacturer brands (national brands) and retailer house brands (store brands) in the consumer packaged goods sector in a highly concentrated grocery retail environment. Of special interest is the degree to which the market mechanism is still at play in this kind of environment where retail chains wield considerable power over manufacturers supplying the respective grocery retail categories. The study focuses on two consumer packaged goods categories, and data collection is conducted via a combination of in-store category observation and in-depth interviews. The results of in-store category observation data indicate that the shelf space occupied by retailer house brands is largely proportional to the market share of the retailer house brands, which tends to negate the possibility of abuse of power within the product categories studied. Analysis of research interview data unveiled a number of themes that seem to collectively indicate that, both the manufacturer brand and the retailer house brand will continue to have a home in the respective categories, and performance on the part of manufacturer brands is expected for them to be able to justify occupation of valuable shelf space ahead of other competing manufacturer brands in the tightly contested shelf arena. The study points to the importance of participation of both manufacturer and retailer house brands if optimum category performance is to be achieved.